How is Sage a "a bit of a weak healer"?
The oGCD toolkit is powerful with lots of mitigation baked in on top of the pretty high healing potencies and unlike their shield healer counterpart SCH, they can preshield on the run between pulls or while the tank is still gathering mobs whenever they want. Haima is like a mini tank invuln in leveling dungeons, Panhaima is also great for the tank alone, you can constantly have 10% mitigation on the tank, constant auto heals from Kardia and has much higher aoe dps than AST or SCH. It's only outclassed by WHM if they have Misery already charged from dumping Lilies before and more or less on par without one or if its build up during the pull. Between 70-80 Sage gets a lot of additional strong abilities and Pneuma with Zoe is a 900 potency burst heal at level cap.